import java.util.concurrent.locks.Lock; 
import java.util.concurrent.locks.ReentrantLock; 
/* 
 * Lock lock = new ReentrantLock(); 
 * lock.lock();  lock.unLock(); 
 * 類似于 synchronized，但不能與synchronized 混用 
 */ 
public class LockTest { 
  public static void main(String[] args) { 
    final Outer outer = new LockTest().new Outer(); 
    new Thread(new Runnable() { 
 
      @Override 
      public void run() { 
        // TODO Auto-generated method stub 
        while (true) { 
          outer.out1("zhangxiaoxiao"); 
          outer.out2("lihuoming"); 
        } 
      } 
 
    }).start(); 
    new Thread(new Runnable() { 
 
      @Override 
      public void run() { 
        // TODO Auto-generated method stub 
        while (true) { 
          outer.out1("zhangxiaoxiao"); 
          outer.out2("lihuoming"); 
        } 
      } 
 
    }).start(); 
 
  } 
  class Outer { 
    Lock lock = new ReentrantLock(); 
    void out1(String name) { 
      lock.lock(); 
      int len = name.length(); 
      for (int i = 0; i < len; i++) { 
        System.out.print(name.charAt(i)); 
      } 
      System.out.println(); 
      lock.unlock(); 
    } 
    void out2(String name) { 
      lock.lock(); 
      int len = name.length(); 
      for (int i = 0; i < len; i++) { 
        System.out.print(name.charAt(i)); 
      } 
      System.out.println(); 
      lock.unlock(); 
    } 
  } 
} 

import java.util.HashMap; 
import java.util.Map; 
import java.util.concurrent.locks.ReadWriteLock; 
import java.util.concurrent.locks.ReentrantReadWriteLock; 
/* 
 * 問題：設計一個 緩存機制 的 偽代碼 
 *  從集合中讀取數(shù)據(jù)，讀取不到，就寫入，再考慮多線程并發(fā)的情況  
 */ 
public class ReadWriteLockTest2 { 
  private Map<String, Object> data = new HashMap<String, Object>(); 
  private ReadWriteLock lock = new ReentrantReadWriteLock();  
  //讀寫鎖 
  public Object getInstance1(String key, Object obj) { 
    lock.readLock().lock(); 
    Object value = null; 
    try { 
      value = data.get(key); 
      if (value == null) {//一條線程進入這里， 
        lock.readLock().unlock();//讀鎖解了，其他線程就可能也到這了 
        lock.writeLock().lock();//只能有一條線程到這，寫鎖開啟，要寫入數(shù)據(jù)了 
        if (data.get(key) == null) { 
          value = obj;   
            /*先判斷數(shù)據(jù)，如果不存在，才寫入，，因為 界時當寫鎖解除后，其他 
              線程，再想寫入時， 判斷到數(shù)據(jù)存在 ，就跳過了。就不會發(fā)生同時寫入的情況 
            */    
          data.put(key, value);  
        } 
        lock.writeLock().unlock();//寫完了，解鎖 
        lock.readLock().lock(); 
      } 
    } finally { 
      lock.readLock().unlock(); 
    }   
    return value; 
  }